The following discussion of the prior art is intended to present the invention in an appropriate technical context and allow its significance to be properly appreciated. Unless clearly indicated to the contrary, however, reference to any prior art in this specification should be construed as an admission that such art is widely known or forms part of common general knowledge in the field.
Brexpiprazole, an atypical antipsychotic, is available as REXULTI® (brexpiprazole) tablets. It was developed by Otsuka Pharm Co Ltd. Brexpiprazole is chemically known as 7-{4-[4-(1-benzothiophen-4-yl) piperazin-1-yl] butoxy} quinolin-2(1H)-one of Formula (I).

U.S. Pat. No. 7,888,362 B2 (US '362 B2) discloses brexpiprazole and process for its preparation. The brexpiprazole prepared by the process disclosed in US '362 B2 provides higher levels of impurities which are difficult to separate even by purifications mentioned therein. The brexpiprazole obtained by the process of US '362 B2 is having purity of 91.82% by HPLC, which upon purification by the methods reported therein provides a purity of 95.11% by HPLC. The starting material, compound of Formula (V) was found to the level of 1.0% after purification. Thus, the process disclosed in US '362 B2 provides brexpiprazole with higher impurity levels which may not be suitable for formulations.
International PCT Publication Nos. WO 2013/015456 A1, WO 2015/054976 A1 and WO 2017/025987A1 discloses processes for the preparation of brexpiprazole, intermediates and salts thereof.
International PCT Publication No. WO 2013/162046 A1 discloses dihydrate of 7-[4-(4-benzo[b]thiophen-4-yl-piperazin-1-yl)butoxy]-1H-quinolin-2-one or salt thereof and process for preparation thereof.
Chinese Publication Nos. CN 104829602 A, CN 104844585 A, CN 105061414 A, CN 105175401 A, CN 105399736 A, CN 105440026 A, CN 105461704 A, CN 105461703 A, CN 105541819 A, CN 105859703 A and CN 106188023 A discloses processes for the preparation of brexpiprazole and intermediates thereof.
Chinese Publication No. CN 104844586 A discloses amorphous brexpiprazole and a preparation method thereof.
Chinese Publication No. CN 104829603 A discloses crystal form A of brexpiprazole hydrochloride and process for preparation thereof.
The reported processes disclosed in the art involve several chemical steps and provide the product in a very low yield and higher impurity levels. This results into an expensive process for the preparation of the brexpiprazole and intermediates thereof.
In view of the above, the present invention provides a process for the preparation of pure brexpiprazole in high purity and having lower level of one or more impurities.